Uncoupling elements are installed as spacers in exhaust gas lines of motor vehicles in order to uncouple motions and vibrations to the extent possible. The uncoupling element has a movable bellows made of metal for this, which has a spiral wound metallic hose in the inner area for the purpose of ducting exhaust gas and of protecting the bellows.
After treatment of the exhaust gases, e.g., by means of soot particle filters, is increasingly necessary in modern exhaust systems. In order for such devices to operate in a useful manner, the exhaust gases must have high temperatures. To guarantee, on the one hand, minimum heat loss from the engine outlet to the filter inlet and, on the other hand, to heat-insulate the sensitive bellows against the hot exhaust gas fluid, more or less elastic mats are integrated for insulation in various radial layers within the uncoupling element. Such a heat insulation is known from DE 10 2007 043 944 A1, in which a flexible line element with combined heat insulation and vibration damping is described. A layer built up of a plurality of layers with the shape of a hollow cylinder is arranged between a flexible inner part carrying the exhaust gases and a flexible, gas-tight jacket part.
The drawback of this and similar structural shapes is, on the one hand, reduced flexibility of the uncoupling element and, on the other hand, short service life of the insulation layer, because this does not have the flexibility of the uncoupling element and is heavily stressed by continual vibrations of the exhaust system. The materials used for the insulation must absorb great expansions due to their hollow cylindrical shape during the absorption of motions of the hose. This additionally greatly limits the selection of suitable materials, especially of heat-resistant materials.